Certain uses of D.C. motors require that a motor be capable of operating in both a forward rotational sense and in a reverse totational sense, with the desired sense of rotation being selected by the appropriate operation of switches, Examples of such uses are power windowlift motors and power seat motors for automotive vehicles.
An example of one D.C. motor type is a bifilar wound field type that is operable in a desired sense by selecting a particular one of two inputs. Each input contains a respective on-off switch. When one switch is operated closed while the other remains open, a respective magnetic field is created causing forward motor rotation. When the other switch is operated closed while the one remains open, a respective magnetic field is created causing reverse motor rotation. Although only two switches are required in this example, their current-carrying capacity must necessarily be increased as the current rating of the motor is increased. The cost of such higher-current switches may increases in relation to motor cost in a way that decreases the cost-effectiveness of the motor and the associated switch curcuit.
Another type of D.C. motor and associated switch circuit that provides bi-directional motor rotation is a permanent magnet D.C. motor connected to an "H" bridge switch circuit, The "H" bridge comprises four switches, two connected to one motor terminal and two connected to the other motor terminal. The switches are operated in a manner to cause the armature current to flow in either a forward direction or a reverse direction, thereby causing forward or reverse motor rotation. Although a permanent magnet D.C. motor may afford certain advantages, its association with an "H" bridge circuit that contains four switches in order to endow it with a bi-directional rotational capability may, as in the preceding example, result in decreased cost-effectiveness for the motor and associated switch circuit as current-carrying requirements increase.
Cost-effectiveness may be a significant factor in mass-production of such motors and curcuit, especially for automotive usage, as in the exemplary power windowlift and power seat uses mentioned above.
The present invention relates to novel D.C. electric motors and associated switch circuits for selecting forward and reverse motor rotation. In certain uses, such motors and circuits may offer opportunities for better cost-effectiveness in comparison to other motors and circuits in these same uses.
The foregoing, along with further features, advantages, and benefits of the invention, will be disclosed in, and perceived by the reader from, the following detailed description of a presently preferred embodiment of the invention representing the best mode contemplated at this time for carrying out the invention. The disclosure is accompanied by drawings, described briefly as follows.